1. Field of the Invention
The present invention relates to optical glass, a press-molding glass material and an optical element which are comprised of the optical glass, and a method of manufacturing an optical element employing the press-molding glass material.
2. Discussion of the Background
In recent years, as image pickup devices have achieved ever greater functionality and become ever more compact, the demand for lenses made of high refractive index glass has increased. For example, the optical glasses disclosed in Document 1 (Japanese Unexamined Patent Publication (KOKAI) No. 2009-120485) and Document 2 (Japanese Unexamined Patent Publication (KOKAI) No. 2006-219365) or English language family members US2008/254965A1 and U.S. Pat. No. 7,897,531, which are expressly incorporated herein by reference in their entirety, are known as such lens materials.
However, based on investigation by the present inventor, conventional high refractive index glasses, including the optical glasses described in Documents 1 and 2, present various manufacturing problems. These include having a high glass transition temperature, which renders the glass unsuited to precision press molding; the necessity for a high annealing temperature, subjecting the annealing furnace to wear and tear; and having a high liquidus temperature, compromising manufacturing stability.